In their time they were among the most striking sights in the sky -- great, floating airships, as big as ocean liners.
The U.S. Navy hoped the USS Macon and other dirigibles like it would act as flying aircraft carriers. A dirigible could hide in the clouds and lower a gondola to spy in enemies below.
The Macon could even carry five small biplanes -- releasing them in midair for reconnaissance flights, and then catching them when they returned from their missions.
'The Most Stunning Thing'
It may sound audacious now, but not then. "Having a flying aircraft carrier with planes on board made sense," said Robert Schwemmer, who heads the west-coast office of the Marine Heritage Program at the National Oceanic and Atmospheric Administration. "You had planes that would extend the scouting range of the airship. With their belly tanks, they could be launched and travel 200 miles from the airship."
Designers were so confident of the concept that the tiny Sparrow Hawk scout planes had no landing gear.
"I think those dirigibles were probably the most stunning thing you could probably see back in the '30s," said Christopher Grech, who has researched the Macon for 20 years as part of his job at the Monterey Bay Aquarium Research Institute in California.
"It actually had eight engines, and the sound it would make was incredible," he said. "They'd cast these huge shadows, and kids would be chasing the shadows on the ground."
All that is a thing of the past. Today the Macon lies in a thousand feet of water off the California coast, brought down in a storm in 1935.
All but two of its 83 crew members survived, but the Navy's experiment with military dirigibles ended with the Macon. Its sister ship, the USS Akron, had crashed off Atlantic City, N.J., in 1933, killing 73 of its 76 crew members. An earlier ship, the Shenandoah, had crashed in 1925.
(The Navy used helium to keep its airships in the sky. It decided against hydrogen, more buoyant but highly explosive, which would destroy the German Hindenburg in 1937.)
Now, a research vessel has been sent to explore the Macon. Christopher Grech and a team of researchers have set out in the R/V Western Flyer, a 118-foot ship specially designed to remain stable in rough seas.
On a five-day mission, it is deploying a robot submersible, the Tiburon, to conduct a survey of the Macon's resting place. The Tiburon will catalog everything to be found at the wreck site. It is equipped with high-definition cameras, and powerful thrusters to keep it stable in ocean currents.
It is a race against time. The Macon weighted 400,000 pounds and was 785 feet long, with 75 miles of aluminum girders to support its frame, but aluminum does not do well in salt water. The wreck has decayed significantly since a commercial fisherman accidentally snagged a piece of it in the late 1980s.
But it has gone virtually undisturbed since it sank, which is tantalizing to researchers.
"It's a time capsule," said NOAA's Schwemmer. "It's definitely a snapshot of a bygone era."
Today the idea of a dirigible for reconnaissance feels almost quaint; satellites, drones and supersonic jets can do the job much more easily.
But in the early '30s, the Macon was high technology. Scientists want to learn all they can about it, before the wreck dissolves in the sea.
"The Macon," said Schwemmer, "is a pretty incredible airship."